Diversity receiver indicator circuit



Dec. 2,' '1952' A. D. zAPPAcosTA 2,620,437

DIVERSITY RECEIVER INDICATOR CIRCUIT Filed OC'. 9, 1950 Y! :jf Y@ ATTORNEY Patented Dec. 2, 1952 2.620,4?,7l D-IvERsIrY RECEIVER INDIUTOR CIRCUIT Amedeo D. Zappacosta, Havertown*Pa.assigner toA Radio Corporation of Americas, acorp'oration f of Delaware Application october 9, 1950, AVserial No. 1891,111

1 Claim. l .This invention' relates-tol aldiversity receiver indicator circuit, and `more particularly 'tofa dual diversityreceiver signal intensity :comparator circuit. l

Recently, rather inexpensive dual diversity controlled, thatr i's,v arev bothiftuned by means of a-single-tuningicontrol.

Forproper operation of dual .diversityfhomereoeivers of the foregoing type, 'it is essential that the tworeceivers Ybe initially adjusted to vhave substantially yequal outputs under'optimum vreceiving conditions, and also that they each be adjusted to havemaximumgain under such conditions. In order to effect such initial. adjustment, `a circuitfor comparing the signal intensities vinthe two receivers must be provided.. Prior to this invention, one rather well-known type: of signal intensitycomparator' circuit: 4has. included atl-least two Vmicro-ammeters, one-connected to be responsive to the signal intensity in 4eachof the .two respectiveV receivers. The prior arrangementswere quite expensive, vcausing theitotalfcost of the unit to be unduly high. Moreover, thefarrangements are in vmost cases usedfonly once (for initial .adjustment of Vthe twoV receivers), being used again infrequently, ifat all. Because Iof their high rst. cost and extremely infrequent utilization, prior arrangements which. include micro-ammeters are rather impractical for use in lhome-typev diversity receivers,.rwhere costs must be. keptl to 'a minimum-ina competitive market. These priory measuring .instruments have yanother-drawback `which militatesr against their use` in homereceivers. Micro-ammetersemphasize the quantitative"indication-'of signal in'- tens'ity, calling for-morefmentalieffort to makey an intensity comparison than if the qualitativer-in dication 'were' emphasized. 'It is Aquite important that home receivers be capable of adjustmentzand operation with a minimum of mental effort.-

An object -of' this invention is to provide-asini'- Reception infthese' (Cl. 250k-e270);

ple *and relatively inexpensive. 'signal intensity comparator leTcircuit "-for ruse -in dual diversity receivers, partieularlylthosel adaptedffor home use.

'Another-objectifs -to" devise a signa'l `ii'itensit-y comparator cir-cuit -whichf gives' 'aqual'itative iindication of signal equality, 'thus reduci'ngthe mental effort' required for utilization of the cir- 'The foregoingland other 'objects of the invention vfvvill be best understood 'from the following description of'an exemplification thereof, reference -being had to the accompanying drawing. wherein thesingle figure is a diagrammatic represen-tation of a. circuit according -to this invention.

The objectsof this invention are accomplished, briefly, in-theifollowing manner: the intermediate frequency outputsfof two radio receivers are'connected to a common diode load for utilization purposes. An velectron-ray tube having two raycontrol electrodes is utilized, the currentsupplied by each receiver to the common load being applied separately, through an amplifier, to-a corresponding one of the ray-control electrodes of such tube.. The angular width Vof the shadow cast by'each control electrode on the tube target gvesia: qualitative visual indication of the signal intensity inthecorresponding receiver. The inten'sitiesof the two signals'are compared by visually comparing the angular widths of the two shadows on. the tube target.

'In vthe drawing, a receiving antenna I feeds input' to a tunable radio frequency amplifier 2, the output of which is fed through another tunable radio frequency amplifier 3 to a lmixer 4 to vwhich are v also ksupplied oscillations from la suitable oscillator 5. This is a more or less conventional superheterodyneA receiver arrangement, the vmixer 4 supplying intermediate frequency energy t'o. an .intermediate frequency amplifier 6. ElementsA I', 2, 3, 4 and 6 may be thought of as comprisinga first radiok receiver. A secondsimilarV radio-'receiver 1', 8, 9, I0 and II is utilized. Receivingl antenna 1; which is in space or polarization diversity with respect to antenna. I, Afeeds input to a tunable radio frequency am-plier 8,

theoutpu-t of which is fed through another tunable -radio frequency amplifier 9 to a mixer III to which Vare also :supplied oscillations. from' oscillator '5 which lis commento both receivers. Mixer |10 supplies Vintermediatefrequency energy to an: intermediate frequency amplifier I I. The second" radio receiver 'l to H- is also aj superheterodyne receiver and lis arranged -in diversity with respect ltothev rst' receiver. Unitsr 21,73, 5,

8 and 9 are unicontrolled for tuning purposes, as indicated by the dotted lines, and are operated by a single tuning control knob, indicated at I2. This is a more or less conventional arrangement.

The output of intermediate frequency amplifier 6 is applied to the primary I3 of a. coupling transformer I4, the secondary I of which is tuned by a capacitor I6. One end of secondary I5 is bypassed to ground for intermediate frequencies by condenser I1. The intermediate frequency energy appearing in winding I5 is rectied or detected by a diode I8 the anode of which is connected to the upper end of winding I5 and the cathode of which is connected through a load resistor I9 to ground, a second load resistor 29 being connected effectively in series with resistor I9, between ground and the lower end of winding I5. The detec-ted voltage of audio frequency derived from amplifier 6 appears across resistor 20, which is common to the two receivers and therefore constitutes a common diode load. Leads. 2 I connected to resistor 20, supply the usefulaudio output to an audio amplifier and utillzationdevice 22, of any suitable type.

' Similarly, the output of intermediate frequency amplifier I I. isapplied to the primary 23 of a coupling transformer 24, the secondary 25 of which is tuned by a capacitor 26. One end of secondary 25 is bypassed to ground for intermediate frequencies by condenser 21. The intermediate frequency' energy appearing in winding 25 is rectifed or detected by a diode 28 the anode of whichV is connected to the upper end of winding 25 and the cathode of which is connected through a load resistor 29 to ground, load resistor 20 being connected effectively also in series with resistor'29, between ground and the lower end of wind-ingl 25. The detected voltage of audio frequency derived from amplifier II also appears across resistor 26. Therefore, the two radio receivers are both connected to supply audio frequency energy to the common diode load 29 and v the unit 22. By this arrangement, diversity action is produced in unit 22 and most of the disadvantagesl resulting from fading are eliminated.

Y 'Although diodes I8 and 28 are illustrated as being separate tubes, it will be appreciated that these two diodes maytogether be a single tube of the twin-diode type, such as 6H6, for example, These diodes are illustrative of any suitable rectifiers which may be used. such as for example selenium or germanium or copper oxide rectiiiers.

It may be seen that a voltage proportional to the current lsupplied by the first receiver to common load 20 appears across resistor I 9, while a voltage proportional to the current supplied by the second receiver to common load 29 appears across resistor 29. Prior to this invention, the current supplied by each receiver to the common 'load'was usuallyV measured by an individual micro-ammeter. However, according to this invention electronic visual indications of the two separate currents are provided.

' The voltage across resistor I9 is applied through Va resistor 30 to onercontrol grid 3| of a twintriode tube 32 connected to operate as two separate direct current amplifiers. Tube 32 may, for example, be of the 6SN7 type. An intermediate frequency bypass condenser 33 is connected from grid 3| to ground. The right hand anode 34l of tube 32 is connected through a load resistor 35 to a source of positive potential. Grid bias is provided by connecting the two -cathodes -of tube 32 together and to the junction point of two series-connected voltage divider resistors 36 and 37, which are placed across the source of positive potential.

The ampliiied potential at anode 34 is applied to one ray-control electrode 38 of an electronray tube 39. Tube 39 is preferably of the 6AF6-G twin-indicator type, and includes two ray-control electrodes 38 and 40, a heated cathode 4I and a target anode 42. Cathode 4I is grounded and target anode 42 is connected to the positive potential source, as indicated.

With no signal in the rst receiver (no voltage across resistor I9) the angular width of the shadow produced by electrode 38 on target 42 is relatively large. As signal comes in and increases in amplitude,l the angular width of such shadow decreases, having its minimum width in response to maximum voltage across resistor I9. The angular width of this shadow, therefore, provides a qualitative visual indication of the intermediate frequency signal intensity in the first radio receiverindicating the current suppled by the receiver 2, 3, 4, 6 to the common load 29.

The voltage across resistor 29 is applied through a resistor 43 tothe other control grid 44 of tube 32. An intermediate frequency bypass condenser 45 Vis, connected from grid 44 to ground. The left hand anode 46 of tube 32 is `connected through a load resistor 4'1 to the source of positive potential.

The amplified potential at anode 46 is applied to ray-control electrode 40 of tube 39. With no signal in the second receiver (no voltage across resistorV 29) the angular width of the shadow produced by electrode 40 on target 42 is relatively large. As signal comes in and increases in amplitude, the angular vwidth of such shadow decreases, having its minimumY width in response to maximum voltage across resistor 29. The angular width of this shadow, therefore, provides a qualitative visual indication of the intermediate frequency signalintensity in the second radio receiver, indicating the current supplied to the common load 20 by the receiver 8, 9, I0, I I.

'When the system described is in operation, that is, when the two radio receivers are energized, the intensities of the two signals are easily compared yby visually comparing the angular 'widths-of theY two shadows (produced by electrodes 38 and y40) on the tube target 42. Thus, a direct qualitative indication of signal equality is provided, a mini/mum Yof mental eifort being required. v

The 'arrangement described, including the tubes 32 'and 39, is considerably less expensive than prior art arrangements. v

Inoperation, with both receivers energized, the procedure is somewhat as follows. The radio frequency or intermediate frequency gain of the two receivers is adjusted, while observing target 42, until the two shadows observed are each of minimum angular widthand until the two shadows are of substantially equal angular widths. This means that the signal intensities in the two receivers are substantially equal to each other and are both of the desired high intensity. The dual diversity receiver-system can then be operated in the normal manner, for reception of radio programs, until another adjustment is deemed necessary, which underA normal conditions will not be until a quite considerable time after the initial adjustment.

It will thus bevs'efen that the invention provides a very simple arrangement, one which can be used with extreme facility and one which is also very efficient and eiective.

What 1 claim to be my invention is as follows:

A signal intensity comparator circuit for diversity receivers, comprising separate means for detecting the signal output of each receiver and for applying each detected output to a corresponding separate load impedance and also to a load impedance common to all of the receivers, a utilization device coupled to said common impedance to receive detected output from all of the receivers simultaneously, means for producing an electron beam, a pair of beam current con-V trol electrodes in the path of said beam, means for applying the voltage developed across a first separate load impedance to one of said beam current control electrodes, and means for applying the voltage developed across a second separate load impedance to the other of said beam current control electrodes.

AMEDEO D. ZAPPACOSTA.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,874,866 Beverage et al Aug. 30, 1932 1,901,117 Peterson Mar. 14, 1933 2,004,126 Moore June 11, 1935 2,130,485 Feldman et al Sept. 20, 1938 2,296,089 Crosby Sept. 15, 1942 2,451,584 Stone Oct. 19, 1948 

